Thermochromic films based on vanadium dioxide (VO2)/ethylene vinyl acetate copolymer (EVA) composite were developed. The monoclinic VO2 particles was firstly prepared via hydrothermal and calcination processes. The effects of hydrothermal time and tungsten doping agent on crystal structure and morphology of the calcined metal oxides were reported. After that, 1 wt % of the prepared VO2 powder was mixed with EVA compound, using two different mixing processes. It was found that mechanical properties of the EVA/VO2 films prepared by the melt process were superior to those of which prepared by the solution process. On the other hand, percentage visible light transmittance of the solution casted EVA/VO2 film was greater than that of the melt processed composite film. This was related to the different gel content of EVA rubber and state of dispersion and distribution of VO2 within the polymer matrix phase. Thermochromic behaviors and heat reflectance of the EVA/VO2 film were also verified. In overall, this study demonstrated that it was possible to develop a thermochromic film using the polymer composite approach. In this regard, the mixing condition was found to be one of the most important factors affecting morphology and thermo-mechanical properties of the films.

In this study, an alternative approach is presented for developing thermo-chromic film, based on ethylene vinyl acetate copolymer (EVA) and vanadium dioxide (VO2) composite, with enhanced oxidation stability and compatibility. The neat monoclinic nanocrystalline VO2 particles were firstly prepared via a hydrothermal process, using citric acid as a reducing agent. After that, the synthesized VO2 particles were characterized, prior to mixing with maleic anhydride grafted PE. The crystalline structure, morphology and thermochromic performance of the polyethylene coated vanadium dioxide (VO2@PE) particles were then verified by SEM, TEM, DSC, XRD, FTIR techniques. After coating, a better oxidation stability of the VO2 particles was noted while the thermo-chromic performance of the VO2@PE was also maintained. After mixing with EVA, the percentage strain and tensile toughness of the VO2@PE based EVA films was the highest, followed by those of the uncoated VO2-based EVA films and the neat EVA, respectively. The VO2@PE-based films also maintained the thermochromic behavior of the monoclinic VO2. The above improvements were achieved at the expense of percentages of visible light transmittance and gel content of the EVA. This is the first report of the EVA/VO2-based thermo-chromic film, which is tougher and more stable toward oxidation than the prior state of the art. This composite film has the potential to be used as a kind of a specialty lamination material for smart windows and energy efficiency in buildings.

Vanadium dioxide (VO2) particles were modified by grafting with poly(styrene sulfonate) (PSS) and poly(3,4-ethylenedioxythiophene) (PEDOT) via surface-initiated atom transfer radical polymerization (SI-ATRP). Critical transition temperature ( T c ) of the modified VO2 ranging between 77 and 79°C was obtained. After mixing with acrylic-based emulsion, dispersion of the VO2 particles in the polymer matrix was significantly improved. The visible light transmittance through the composite films above 75% was maintained if a concentration of the modified VO2 particles loaded into acrylic polymer film was no greater than 1.0 wt%. The NIR transmittance through the acrylic/VO2@PSS : PEDOT also dropped by 9-10%, compared with that of the pure acrylic film (without any particles). Finally, glass substrates coated with the acrylic/VO2@PSS : PEDOT composite films could reduce the temperature inside a model house by 5-6°C, compared with that of the control system (pure acrylic coating film without VO2 particles). Overall, this work demonstrated that it was possible to improve the dispersion of VO2 particles in polymer films without sacrificing its NIR shielding ability by grafting the surface of VO2 particles with PSS : PEDOT chains, while providing the optimum grafting density and particle loading.

Vanadium dioxide film, to be used as a thermochromic material for smart glazing, were prepared and fabricated on glass substrate via a polymer assisted deposition (PAD). Poly (vinyl pyrrolidone) (PVP) and poly (vinyl alcohol) (PVOH) were used as the film former to control the viscosity of precursor solution and interact with vanadium ions. The structural characteristic of vanadium oxides films was optimized in this work using Taguchi's experimental design. The optimization was performed by considering the effect of annealing temperature, annealing time and heating rates on film thickness and XRD patterns of the prepared film. The results from XRD patterns indicated that the optimum conditions corresponding to the formation of vanadium dioxide (VO2), regardless of the polymer type, is that by using the annealing time and temperature of 6 h and 450 °C, respectively.

This research work concerns the development of phase change materials based on poly(ethylene terephthalate) (PET) mixed with vanadium dioxide particles (VO2). Monoclinic VO2 particles were synthesized via a hydrothermal process followed by modification of the particle surface with a silane coupling agent, namely 3‐(aminopropyl) triethoxysilane (APTES). After that, the metal oxide particles were mixed with PET flakes, derived from used PET bottles, in an internal mixer. In this study, the effects of surface modification and concentrations of VO2 particles on thermomechanical and optical properties of the composites were investigated. From the DSC results, it was found that the percentage crystallinity of PET increased after loading with VO2. This indicates that VO2 can act as a nucleating agent inducing the crystallization of the PET chains. From the scanning electron microscopy with energy dispersive X‐ray spectroscopy (SEM–EDX) images, better dispersion of VO2 particles in the PET matrix was noticed when the surface‐modified VO2 particles were used as a replacement for the normal VO2 particles. This contributed to the greater percentage of visible light transmittance through the composite sheets. Thermogravimetric analysis (TGA) profiles of both PET and PET/VO2 specimens are similar, indicating that the VO2 did not accelerate the thermal decomposition of the PET. When the specimens were exposed to an IR lamp, it was found that the temperature behind the PET/VO2 sheets dropped when compared to that of the neat PET sheets. Some shrinkage and deformation of the PET/VO2 specimens were also noticed. The higher the VO2 loading, the greater the deformation. The effect was ascribed to the fact that the actual temperature was above the critical transition temperature of VO2. Consequently, the NIR transmittance was suppressed at the expense of the greater NIR absorbance by the VO2 phase in the composites. Finally, when the specimens were exposed to solar irradiation at ambient temperature, the temperature underneath the PET/VO2 specimens became greater than that of the control specimen (the neat PET). The result was discussed in the light of the emissivity of VO2 at ambient temperature, which is considerably low. Overall, this study demonstrates that PET/VO2 can exhibit both cooling and warming effects, depending on the ambient temperature in relation to the critical transition temperature (Tc) of VO2.